BACKGROUND: Asthma genetics has been extensively studied and many genes have been associated with the development or severity of this disease. In contrast, the genetic basis of allergic rhinitis (AR) has not been evaluated as extensively. It is well known that asthma is closely related with AR since a large proportion of individuals with asthma also present symptoms of AR, and patients with AR have a 5-6 fold increased risk of developing asthma. Thus, the relevance of asthma candidate genes as predisposing factors for AR is worth investigating. The present study was designed to investigate if SNPs in highly replicated asthma genes are associated with the occurrence of AR.

METHODS: A total of 192 SNPs from 21 asthma candidate genes reported to be associated with asthma in 6 or more unrelated studies were genotyped in a Swedish population with 246 AR patients and 431 controls. Genotypes for 429 SNPs from the same set of genes were also extracted from a Singapore Chinese genome-wide dataset which consisted of 456 AR cases and 486 controls. All SNPs were subsequently analyzed for association with AR and their influence on allergic sensitization to common allergens.

RESULTS: A limited number of potential associations were observed and the overall pattern of P-values corresponds well to the expectations in the absence of an effect. However, in the tests of allele effects in the Chinese population the number of significant P-values exceeds the expectations. The strongest signals were found for SNPs in NPSR1 and CTLA4. In these genes, a total of nine SNPs showed P-values <0.001 with corresponding Q-values <0.05. In the NPSR1 gene some P-values were lower than the Bonferroni correction level. Reanalysis after elimination of all patients with asthmatic symptoms excluded asthma as a confounding factor in our results. Weaker indications were found for IL13 and GSTP1 with respect to sensitization to birch pollen in the Swedish population.

CONCLUSIONS: Genetic variation in the majority of the highly replicated asthma genes were not associated to AR in our populations which suggest that asthma and AR could have less in common than previously anticipated. However, NPSR1 and CTLA4 can be genetic links between AR and asthma and associations of polymorphisms in NPSR1 with AR have not been reported previously.

The practice of restocking already viable populations to increase harvest potential has since long been common in forestry, fisheries and wildlife management. The potential risks of restocking native species have long been overshadowed by the related issue of invasive alien species. However, during the last decade releases of native species with potentially non-native genome have received more attention. A suitable model to study genetic effects of large-scale releases of native species is the Mallard Anas platyrhynchos, being the most widespread duck in the world, largely migratory, and an important quarry species. More than 3 million unfledged hatchlings are released each year around Europe to increase local harvest. The aims of this study were to determine if wild and released farmed Mallards differ genetically, if there are signs of previous or ongoing introgression between wild and farmed birds, and if the genetic structure of the wild Mallard population has changed since large-scale releases started in Europe in the 1970s. Using 360 Single Nucleotide Polymorphisms (SNPs) we found that the genetic structure differed among historical wild, present-day wild, and farmed Mallards in Europe. We also found signs of introgression in the wild Mallard population, that is, individuals with a genetic background of farmed stock are part of the present free-living population. Although only a small proportion of the released Mallards appears to survive to merge with the free-living breeding population, their numbers are still so large that the genetic impact may have significance for the wild population in terms of individual survival and longterm fitness.

The practice of restocking already viable populations to improve harvest has since long been common in forestry, fisheries and wildlife management. The potential risks with restocking of native species has for a long time been overshadowed by the related issue of invasive species. However, during the last decade releases of native species with a potential non-native genome have attained more attention. A suitable model species for studying genetic effects of large-scale releases of a native species is the Mallard, Anas platyrhynchos; it is the most widespread duck in the world, it is a migrating species, and an important game bird. In several European countries it is also farmed and released to increase the harvestable population, and more than 3 million unfledged hatchlings are released each year around Europe. The aims of this study were to determine if wild and released farmed Mallards differed genetically among subpopulations in Europe, if there are signs of previous or ongoing introgression between wild and farmed Mallards, and if the genetic structure of the wild Mallard population has changed since large-scale releases started in the 1970s. We used 360 Single Nucleotide Polymorphisms (SNPs) to analyze the genetic structure of historical wild, present-day wild, and farmed Mallards. We found a clear genetic difference between wild and farmed Mallards in Europe. We also found signs of introgression of farmed genes in the wild Mallard population, however, the rate of hybridization is probably minor due to low survival of released farmed Mallards and a change of the wild population since the start of large-scale releases is therefore limited. A low level of hybridization between farmed and wild Mallard is desired as introgressed genes may be detrimental for wild Mallards, and efforts to increase survival of farmed Mallards should therefore not be encouraged.